"Culture" is a very blunt instrument for talking about variation.
A more precise approach was that used by Goodenough in a wonderful old
paper from the early 1970s, when he spoke of language variation. He
pointed out how distinct each individual's use of lnguage could be
(idiolect), how all groups developed their own distinctive dialects, and
then how dialects could be organized various ways into higher order
groups. He also pointed out the that criteria for lumping at some levels
could be used for splitting at others, and vice versa. Which would argue
that 'more' or 'less' variation may not be the issue, as much as the
kinds of variation.